ACPI / hotplug: Fix handle_root_bridge_removal()

It is required to do get_device() on the struct acpi_device in
question before passing it to acpi_bus_hot_remove_device() through
acpi_os_hotplug_execute(), because acpi_bus_hot_remove_device()
calls acpi_scan_hot_remove() that does put_device() on that
object.

The ACPI PCI root removal routine, handle_root_bridge_removal(),
doesn't do that, which may lead to premature freeing of the
device object or to executing put_device() on an object that
has been freed already.

Fix this problem by making handle_root_bridge_removal() use
get_device() as appropriate.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Cc: All applicable <stable@vger.kernel.org>

drivers/acpi/pci_root.c

@@ -608,9 +608,12 @@ static void handle_root_bridge_removal(struct acpi_device *device)
 	ej_event->device = device;
 	ej_event->event = ACPI_NOTIFY_EJECT_REQUEST;
 
+	get_device(&device->dev);
 	status = acpi_os_hotplug_execute(acpi_bus_hot_remove_device, ej_event);
-	if (ACPI_FAILURE(status))
+	if (ACPI_FAILURE(status)) {
+		put_device(&device->dev);
 		kfree(ej_event);
+	}
 }
 
 static void _handle_hotplug_event_root(struct work_struct *work)